Abstract

The effect of digitalis on the rest and exercise hemodynamics of eight normal subjects was studied. Cardiac output was determined by the dye dilution technique, using a cuvette densitometer. Arterial and venous pressures were measured on Statham strain gauges. Data were obtained during rest and exercise before and after intravenous administration of 1.0–1.2 mg of digoxin or 1.6–1.8 mg of acetyl strophanthidin. At rest there was a decrease of cardiac output (average 12%), pulse rate (5%) and stroke volume (9%) and an average rise of blood pressure from 129/73 mm Hg (mean 95 mm Hg) to 156/86 mm Hg (mean 109 mm Hg) following digitalization. During exercise there was a decrease of cardiac output (average 18%), pulse rate (6%) and stroke volume (9%), but no change of blood pressure after digitalization. The systemic vascular resistance was increased following digitalization, both during rest and exercise. In three additional subjects, the blood pressure rise accompanying digitalization at rest was verified by demonstrating a prompt increase in blood pressure as acetyl strophanthidin was injected and a fall as the control saline injection was resumed. Since the positive inotropic action of digitalis explained neither the rise of systemic vascular resistance nor the fall of cardiac output following digitalization of normal subjects, a peripheral action of cardiac glycosides was suggested. It is concluded that whatever augmentation of myocardial contractility that may result from digitalization of the resting or exercising normal subject is overshadowed by the peripheral action of the drug.